Field of the Invention
The present invention relates to pneumatic tires, and in particular relates to a winter tire that may improve steering stability on dry, ice and snow, in well balanced manner.
Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2006-298202 discloses a winter tire having an improved traction on snow. The winter tire includes a tread portion having a block pattern including a plurality of blocks separated by a plurality of circumferential and continuously extending main grooves and a plurality of lateral grooves. This tread pattern may offer grip in the circumferential direction by snow-shearing force obtained through the lateral grooves, and therefore traction and braking performance on snow can be achieved. Furthermore, the tread pattern may also offer lateral grip by snow-shearing force obtained through the main grooves, and therefore steering stability on snow can be achieved. Note that the concept of steering stability means not only cornering performance but also straight traveling stability.
In general, reaction force from the ground acting on the tread portion, when straight traveling or braking, would act on the lateral grooves mainly, and would be hardly to act on the circumferential main grooves. On the other hand, reaction force from the ground acting on the tread portion, when cornering, would act on the main grooves mainly, and would be hardly to act on the lateral grooves. Accordingly, there is a tendency where the main grooves and the lateral grooves function independently, and snow pillar compressed in either grooves tends to break easily. Thus, there was a problem that the above mentioned conventional tire may not offer sufficient traveling performance on snow.